1. Technical Field
The present invention relates to a variable magnification projection optical system and a projection display apparatus, and more specifically to a two-group variable magnification projection optical system suitable for magnifying and projecting a light beam having image information from, for example, a light valve onto a screen, and a projection display apparatus equipped with the same.
2. Background Art
Recently, projection display devices that use light valves, such as liquid crystal display devices and DMD (Digital Micro-Mirror Device: registered trade mark) display devices have been widely used. In particular, those that use three light valves corresponding to each of the three primary colors of R (red), G (green), B (blue) to modulate each illumination light, then combine the light modulated by the respective light values by, for example, a color combining prism, and display an image on a screen via a projection lens have been widely used.
As downsizing and high definition have advanced rapidly in such light valves, the demand for presentation using such projection display devices has also been increasing with a wide spread use of personal computers, and as those which are user-friendly and ease of installation are anticipated, the demand for a more compact and light weight projection display device having a higher performance with a higher magnification ratio is increasing. Further, along with this, a strong demand exists for more compact and light weight projection lenses having a higher performance with a higher magnification ratio. Further, at the same time, a strong demand for cost reduction in projection lenses also exists.
In the meantime, in a case where a color combining prism for combining modulated light from a plurality of light valves or a TIR (Total Internal Reflection) prism used for separating illumination light from projection light is disposed in an optical system, the reduction side of the projection lens is required to be telecentric in order to prevent generation of color unevenness in the former case and to prevent degradation in separation efficiency in the latter case.
As for the projection lenses used in such projection display devices, variable magnification optical systems capable of changing the size of a projected image on a screen are often used. Conventionally, telecentric variable magnification optical systems with four or five lens groups have often been used, and if a higher performance or a higher magnification is required, a variable magnification optical system with six lens groups has been used. But, such a multiple group configuration is undesirable for pursuing reduction in size, weight, and cost, since the configuration is complicated.
Consequently, Japanese Unexamined Patent Publication No. 2010-113150 proposes a zoom lens as a simply configured two group zoom lens. The zoom lens described in Japanese Unexamined Patent Publication No. 2010-113150 includes a first lens group having a negative refractive power and a second lens group having a positive refractive power disposed in order from the magnification side and is configured such that the two lens groups are moved in an optical axis direction during magnification change.